The present invention relates to an electrode lead body for high energy systems using implantable electrodes, and specifically to an electrode lead body which maintains insulation and spacing between two conductors housed by the lead.
In implantable systems such as cardiac pacemakers and defibrillators, it is necessary to connect electrodes mounted on or about the heart with cardiac analysis, pacemaking, or defibrillating circuitry. The electrodes may be used for sensing or for delivering electrical energy to the heart. In procedures such as catheter ablation, a catheter lead is required to connect a source of electrical energy to a discharge electrode to be used proximate the myocardium. Regardless of the particular type or use of the electrodes, the lead which connects the electrodes with the circuitry will likely travel through tortuous and winding paths in the body.
In some applications, the lead must carry within it two or more insulated conductors for operatively connecting the electrodes with associated circuitry. A typical lead path begins at the point of connection to the pulse generator, just beneath the skin, and tunnels around the ribs into the thorax to a position in, on or about the heart. At relatively extreme bends in leads of circular cross section, such as may, for example, be encountered where a lead is bent around a patient's first rib, between the first rib and the clavicle, the insulated conductors could be pushed together by the bending forces. Although each conductor is insulated, the insulation is a thin layer of material so as to minimize the overall cross section of the lead, and at times the leads could be separated by only two thicknesses of insulation.
While thin layers of insulative material generally are suitable to separate conductors for sensing and pacing functions, such is not the case when high energy cardioverting or defibrillating pulses are being delivered. High energy discharges are capable of causing arcing between closely spaced conductors, even if the conductors are not touching one another and are insulated. While such arcing may occur in ablation procedures and is conceivable in pacing, it is a particular problem for high-energy applications like cardioversion and defibrillation. Typically, a pacemaker delivers energy levels on the order of microjoules through its lead assembly. A cardioverter or defibrillator, by contrast, delivers much higher energy levels, on the order of joules. Consequently, when delivering such higher-energy cardioverting electrical discharges, a short circuit can be created by arcing across the two insulated conductors if the conductors are forced toward another along the lead extreme bends.
Some pacing lead designs provide a solid lead body having small lumens therein for carrying conductors; see, for example, U.S. Pat. Nos. 3,348,548 to Chardack, 3,949,757 to Sabel and 4,608,986 to Bernek et al. Further, Fisher et al., U.S. Pat. No. 3,333,045, discloses a lead assembly for pacing in which one embodiment apparently includes an oval-shapped outer sheathing surrounding two insulated helical cables. Yet, none of these designs provides a sheathing for avoiding cable/insulation compression against adjoining cable/insulation at extreme bends, such protection being unnecessary for designs directed to lower-energy pacing applications. There thus remains the need for an improved high-energy lead design.